Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/15/2003
Publication Date: 1/1/2004
Citation: Ryan, J.A., Berti, W.R., Brown, S.L., Casteel, S.W., Chaney, R.L., Doolan, M., Grevatt, P., Hallfrisch, J.G., Maddaloni, M., Mosby, D. 2004. Reducing children's risk to soil lead: summary of a field experiment. Journal of Environmental Science and Technology. 38(1):18A-24A. Interpretive Summary: Soils rich in lead (Pb) comprise risk to children who ingest soil and dust from their environment. Many areas of high Pb soils occur in cities near painted surfaces, near heavily trafficked roads, and near Pb-using industries. A cooperative experiment was undertaken to test whether treating the Pb rich soil in a Joplin, MO, vacant lot with about 3000 mg Pb/kg soil could reduce the bioavailability of soil Pb to monogastric animals. Soil was treated with triple super phosphate, rock phosphate, phosphoric acid, biosolids compost rich in Fe, and a mixture of an iron rich byproduct and phosphate, returned to about pH 7.0, and seeded with tall fescue. During the next 3 years the grass and soil were sampled to assess changes in bioavailability of soil Pb to rats, pigs, and humans, chemical extractability of the soil Pb, and physicochemical forms of Pb present in the treated soils. Additions of phosphate without Fe caused much of the soil Pb to become chloropyromorphite, a Pb mineral with very low solubility, whereas when both Fe-oxide and P were added, a mixture of strongly adsorbed Pb bound to Fe, and chloropyromorphite were formed. At 3 years the bioavailability of soil Pb in the phosphate treatment was reduced by about 70% to pigs and humans compared to the untreated soil. An in vitro chemical extraction to assess bioavailability was conducted at pH 1.5, 2.0, and 2.5; at the lower pH, treatments did not change extractability, in strong disagreement with the animal tests. At the higher pH levels, changes in extractability were well correlated with changes in bioavailability. The methods tested in this field test of in situ remediation of soil Pb strongly supports in situ treatment of most Pb contaminated urban soils to protect children from contaminated soils.
Technical Abstract: Traditional methods for reducing risk from elevated levels of soil Pb involves removal, covering, or dilution by mixing with uncontaminated soil. Believing that in situ remediation techniques are viable alternatives, the EPAs National Risk Management Research Laboratory (NRMRL) and DuPont Corporation established a field experiment at a Pb-contaminated urban site in Joplin, MO as part of a collaborative effort. Reductions in Pb bioavailability (in vivo and in vitro) and changes in Pb geochemistry observed as a result of in situ treatment with phosphate sources and with high Fe biosolids compost demonstrate that reduction in soil Pb risk can be accomplished without soil removal.